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https://github.com/wkharold/jobd


https://github.com/wkharold/jobd

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README 

        
#jobd



Jobd implements *cron* as a 9p file system. 9p is [a simple file protocol to

build sane distributed systems](http://9p.cat-v.org/). It's the cornerstone of

[the Styx Architecture for Distributed

Systems](http://doc.cat-v.org/inferno/4th_edition/styx) which represents the

system's resources as a form of file system. Jobd illustrates this approach to

system design using the [go9p](https://code.google.com/p/go9p) library.



##Installation



jobd uses [godep](https://github.com/tools/godep) to capture its dependencies. To install it just

```

$ go get github.com/wkharold/jobd

```

To build it, make sure you have godep installed and then

```

$ godep go install

```



##Usage

```

jobd --help

Usage of jobd:

  -alsologtostderr=false: log to standard error as well as files

  -dbdir="/var/lib/jobd": Location of the jobd jobs database

  -debug=false: 9p debugging to stderr

  -fsaddr="0.0.0.0:5640": Address where job file service listens for connections

  -log_backtrace_at=:0: when logging hits line file:N, emit a stack trace

  -log_dir="": If non-empty, write log files in this directory

  -logtostderr=false: log to standard error instead of files

  -stderrthreshold=0: logs at or above this threshold go to stderr

  -v=0: log level for V logs

  -vmodule=: comma-separated list of pattern=N settings for file-filtered logging

```



Once jobd is started the file system it provides can be mounted via

```

$ mount -t 9p -o protocol=tcp,port=5640  

```

Where **addr** is the IP address of the box running jobd. Note that it needn't be mounted on the machine running jobd, any box running a Linux 3.x kernel should suffice. 



##Design



*cron* is a time-based job scheduler, it has two primary concerns: *jobs* which are commands to be executed, and *schedules* that determine when a job is run. The design of a 9p-based application or system service generally begins with the creation of a *name space*, think file system subtree, that represents the application's resources in terms of files and directories. 



Jobd represents jobs as subdirectories of  a *jobs* directory. Each *job* subdirectory contains four files:



* the **ctl** file which is used to start and stop the job

* the **cmd** file that records the command the job executes

* the **log** file that is used to retrieve the job's execution history

* the **schedule** file that records the job's schedule and its next scheduled execution time



To start a job, write the string **start** to the *ctl* file

```

$ echo -n start > /jobs//ctl

```

Similarly to stop it write the string **stop** to the *ctl* file

```

$ echo -n stop > /jobs//ctl

```

Read from the *cmd*, *log*, or *schedule* file to retrieve the information they provide

```

$ cat /jobs//cmd

echo hello world

$ cat /jobs//schedule

0 0/5 * * * ? *

$ cat /jobs//log

2014-02-11 09:42:33.454707331 -0600 CST:started

2014-02-11 09:42:35.004655691 -0600 CST:hello world

2014-02-11 09:42:40.003579265 -0600 CST:hello world

2014-02-11 09:42:45.003220637 -0600 CST:hello world

2014-02-11 09:42:50.00294003 -0600 CST:hello world

...

```



Jobd jobs are created via the *clone* file. The *clone* file is a peer of the *jobs* directory in the jobd name space. To create a job write a string of the form: :: to the clone file

```

$ echo -n 'hello:0 0/5 * * * ? *:echo hello world' > /clone

```



##TODO



* support deleting jobs